Template-Encoded Assembly and Adaptive Function in Selenium-Based Molybdenum Chalcoxide Rings.

Controlling both structure and function in inorganic self-assembly remains a major challenge. Here we establish a programmable strategy for constructing selenium-based molybdenum chalcoxides using the [Mo2O2Se2]2+ dimer as a universal building block. The template-directed assembly process produces a complete family of ring architectures (n = 8-16), with nuclearity encoded by the template's geometry and acidity. Selenium incorporation introduces electronic softness that imparts unusual structural flexibility and enables adaptive behaviour. NMR titration experiments reveal host-guest exchange in solution, demonstrating dynamic recognition in these purely inorganic rings. This family of clusters also displays tuneable electrocatalytic hydrogen evolution activity (HER), following the trend Mo8 > Mo12 > Mo10 and consistently outperforming their sulphur analogues. Together, these results define a design framework in which modular assembly, dynamic function, and catalytic activity arise from a common chalcogen-dependent structural logic, opening new avenues for responsive inorganic molecular materials.